Of course, there must have been a period after the first wolf was adopted into a human band when its skull was exactly the same as a wolf’s – because it was a wolf. There was no exact moment of transition from one to the other, and the whole debate has a strong flavour of semantics. The more cautious authors merely refer to these intermediates as ‘canids’ or ‘wolf-dogs’, thereby sidestepping the argument altogether.
A similar conundrum faced archaeologists excavating the nearby site of Trou des Nutons, a cave formed in the limestone hills of the Ardennes by the River Lesse, a tributary of the Meuse. Among the fossils found in the Trou des Nutons were beaver, roe deer, horse, bison and wild sheep, suggesting a later occupation than at Goyet. This was confirmed when another skull of a mystery ‘large canid’ was given a carbon date of 21,800 years BP. This is a surprisingly early date and in the middle of the last Ice Age. But was it the skull of a dog or a wolf?
These skulls from France were subjected to a series of precise measurements of snout-length and width, the length of the tooth row and the size of the flesh-shearing, self-sharpening carnassial teeth that wolves and dogs have where we have molars.
Fossil canid skulls from two archaeological sites in Russia and Ukraine, one at Mezin (Ukraine) and the other at Avdeevo just over the Russian border, were given the same treatment. These two sites were inhabited by early humans who constructed huts of mammoth bones and left behind an abundance of beads and other artefacts carved from mammoth ivory. The objective of the osteometric study of candid fossils from these two sites was to discover whether the remains of these ‘large canids’ differed sufficiently from wolves in their skull morphology to be classified as dogs on their way to domestication rather than unmodified wolves.
To complete the comparisons, the analysis was extended to include later, but still prehistoric, unambiguous fossil dogs from France and Germany. Also included were a selection of modern and fossil wolves from Europe and Asia along with modern dogs from several large breeds including Great Dane, Tibetan Mastiff, Siberian Husky, Chow Chow, Irish Wolfhound, Malinois, Dobermann Pinscher and German Shepherd.1
Comparing multiple skull measurements from dogs of different sizes is a complicated business, and I will spare you the details of the multivariate analysis and go straight to the main conclusion. The Palaeolithic skulls from the oldest sites, including Goyet at 31,700 years BP, had a significantly different shape from modern, or indeed fossil, wolves. This suggests that, even by that early date, these animals were dogs already on the way to modification through ‘domestication’. An alternative explanation, though in my opinion rather less likely, is that these were the skulls of one or more wolf species that later became extinct. As we shall see later, there is other enticing evidence to support the former scenario and suggest that the close association between wolf and man began a very long time ago.
The next layer of evidence about the changing appearance of domesticated dogs comes from the late glacial period around 17,000 years BP, when the ice sheets covering northern Europe were fast retreating. The shrinking tundra no longer supported herds of large prey animals. The climate warmed considerably, rainfall increased and forests covered much of the formerly open tundra. The fauna changed with the landscape and many prey animals disappeared. Mammoths, woolly rhinoceros and their predators, the sabre-tooth tiger and cave bear, were forced into extinction. Others, like the wild horse, reindeer and bison, shifted their ranges. Humans began to spread north, first following the shrinking herds and later, as they entered the Mesolithic period, changing their diet to smaller woodland prey, like wild boar, pine marten, red and roe deer. On the coastal settlements, shellfish became a major source of food and the first boats ventured out to sea to catch fish. Supplementing this meagre protein diet were roots and tubers, insects and snails. The heroics of the mammoth hunt became a thing of the past and life became a gruelling fight for survival.
The close cooperation between human and dogs, by now thoroughly assimilated into human society, continued even though the superbly effective working partnership that had developed in the Upper Palaeolithic was at its best when killing large prey, a practice which by now was rapidly disappearing.
Around 12,000 years BP much smaller dogs made their debut in the fossil record. A team of French archaeologists found the remains of thirty-nine dogs at the Pont d’Ambron rock-shelter in the Dordogne. From an osteometric analysis similar to that carried out at the earlier sites of Goyet and Trou des Nutons in the Ardennes, it was clear that the Pont d’Ambron dogs were considerably smaller. The same was true with the remains excavated at the Montespan cave in the northern foothills of the Pyrenees and at the open-air site of Le Closeau in an old channel of the River Seine.
The authors of the exhaustive paper summarising this body of work confidently concluded that they were dealing with the remains of dogs and not wolves. In France at least, and also in Spain, dogs were clearly changing. In Russia, however, at around the same time, wolf-dogs were still very large. Whether this was a result of separate wolf domestications in the two regions or for some other reason, it was impossible to say. One firm but rather grisly conclusion, drawn from cut-marks on the bones of the Pont d’Ambron dogs, was that they had been butchered and, presumably, cooked and eaten.
As well as the issue of timing, the identification of the geographical location of the wolf–dog transition has absorbed many researchers and continues to do so. The first scenario to be proposed, by a group from the University of Konstanz in Switzerland led by Peter Savolainen, was that the major ‘domestication’ event happened only once, in East Asia.2 This was the conclusion of an mDNA study of 654 dogs from different regions of the world where the focus was on the diversity of sequences. The perfectly sensible rationale was that the highest diversity, that is the highest number of different mDNA lineages, would be found in the places where dogs had been around the longest and had the most time to accumulate new mutations, rather like the islanders in our metaphorical example. Savolainen’s team found mDNA sequence diversity was highest in south-east Asia and located the first ‘domestication’ to the region. This was a very controversial conclusion at the time, and it would be another decade before the debate was settled, although it still rumbles on in some quarters.3
In order to make progress on the vexing issues of timing and location, scientists turned to the DNA that had, incredibly (a word I do not use lightly), survived in fossils. Robert Wayne, who headed the Los Angeles lab, was one of the eclectic bunch of scientists who dared to think, against all reason and common sense, that DNA might survive in fossils. As there was no academic tradition of ancient DNA science and this was an entirely new field, the early pioneers came from all sorts of backgrounds. Svante Pääbo, for example, who went on to sequence Neanderthal DNA, was originally an immunologist with an interest in Egyptology that led him to attempt to extract DNA from mummies in 1985. Ed Golenberg, who claimed in a 1990 Nature article that he had extracted DNA from a 17-million-year-old magnolia leaf, was a botanist. Scott Woodward, in a paper published by Science in 1994, reported DNA extraction from a fossil dinosaur Tyrannosaurus rex from the Cretaceous period entombed in a block of coal. Woodward was a geneticist from Brigham Young University in Utah who went on to run a large genetic genealogy project for the Mormon Church. My own background was in medical genetics, specifically the causes of inherited bone disease. In 1989 my colleagues and I reported the first recovery of ancient bone DNA in Nature.
We met regularly to feel our way in this exciting but tricky field where extravagant claims could be accepted for publication by the very best journals – and, more often than not, be rapidly dismissed. Robert Wayne was a regular attendee at these meetings. He is an evolutionary zoologist with an interest, at the time, in the hybridisation of wolves and coyotes where their ranges overlapped. Robert has gone on to become the pre-eminent scientist in dog genetics, first with work on fossil DNA and then with extensive analyses of the genetic variation in living dog breeds. Much of what we know about the genetics of dog evolution comes from Wayne’s lab in Los Angeles. I was slightly surprised to